An HFC network technology is an economical and practical integrated digital service broadband network access technology. An HFC generally includes three parts: an optical fiber trunk, a coaxial cable branch, and a subscriber distribution network. A program signal from a cable television broadcast station is first transformed into an optical signal to be transmitted on a trunk; then the optical signal is converted into an electrical signal after arriving at a user area; and finally the electrical signal is sent to a user by using a coaxial cable after being distributed by using a distributor. FIG. 1 shows a typical HFC network. As shown in FIG. 1, the HFC network may include the following devices and components: a network management system, a metropolitan area network, a cable modem termination system (CMTS), an optical station, a CM, a set top box (STB) on a user side, a personal computer (PC), an optical fiber cable, a coaxial cable, an amplifier, a tap, and the like. The components are not shown one by one in FIG. 1.
There are many fault problems because an HFC network is exposed outside in a long term. The existing data over cable service interface specification (DOCSIS) 3.1 standard is used to design a powerful proactive network maintenance (PNM) fault diagnosis function for these problems. A CM and a CMTS may be used to detect a line, and the CMTS tests and analyzes a detection result. However, the CMTS can only detect that quality of an upstream signal deteriorates, but cannot learn of an abrupt point indicating that the quality of the upstream signal deteriorates. If the upstream signal may be measured along an upstream channel, the abrupt point indicating that the quality of the upstream signal deteriorates may be obtained through analysis, so as to find a fault location. Considering that the HFC network includes many CMs, the upstream signal can be detected at the CMs.
A method for extending a downstream full band capture (FBC) function of a CM to an upstream is proposed in the prior art, to detect an upstream signal at the CM. A simplified implementation structure of the method is shown in FIG. 2. In the simplified implementation structure, a branch is led out from the front (namely, a point “1” in FIG. 2) of a duplexer, and the other end of the branch is connected to the front (namely, a point “2” in FIG. 2) of a downstream FBC module. When a switch of the branch is closed, an analog-to-digital converter (ADC) of the FBC module may collect upstream noise, so as to analyze the upstream noise. In this way, the CM has functions of upstream noise collection and upstream noise detection.
However, the CM that detects the upstream signal by using the downstream FBC function can usually only detect whether the upstream signal has two limited noise types: intrusion noise outside a carrier and white noise, but cannot detect other fault problems.